Honestly, the one band I truly regret never seeing is Slade. I’ve seen just about a ka-billion bands live in places ranging from teeny clubs to hube stadia. But never got to see Noddy and the boys.
I’ve got the DVD of various live performances and it’s magnificent. What I’d give to watch them perform, especially Kashmir, Stairway to Heaven and Black Dog.
Jeff Beck Group, right at the release of their first album, Truth. Rod Stewart, Ronnie Wood, Mickie Most and El Becko at the height of their powers.
Beyond that - the ones mentioned here - the Beatles, Hendrix (although Monterey Pop is the better choice, per robardin - a friend went and said it was everything they say it was…), Led Zeppelin.
I would add the Stones around Exile - I know, they were whacked on drugs, but to hear Mick Taylor’s leads with the boys on Can’t You Hear Me Knockin’ and All Down the Line would’ve been special…
Geez, where to start…Probaby the Clash, followed by The Ramones in 78 or so, The Minutmen or firehose, The Replacements, Barry and the Remains, The Woggles before Mighty Montague died, The Kaisers, The Ramones, The Dukes of Hamburg, The Mummies, The Sonics, The Monks, The Gories, The Oblivians, Thee Mighty Caesers, MC5, Thee Headcoats.
Just off the top of my head, I’ll think of more later.